Merge branch 'nd/exclusion-regression-fix'

The ignore mechanism saw a few regressions around untracked file
listing and sparse checkout selection areas in 2.7.0; the change
that is responsible for the regression has been reverted.

* nd/exclusion-regression-fix:
  Revert "dir.c: don't exclude whole dir prematurely if neg pattern may match"

diff --cc Documentation/gitignore.txt
Simple merge

diff --cc dir.c
Simple merge

diff --cc t/t3001-ls-files-others-exclude.sh
Simple merge